[Elecraft] K2 CAL FIL: Setting the BFO for the best sounding SSB TX signal.
Gary L Surrency
[email protected]
Mon Apr 15 16:20:03 2002
Some folks have noticed their RX and TX SSB audio is not as good as it
could be. The easiest way to resolve these problems, is to first use
Spectrogram to set the filters up well for RX. See our website for
details on how to do this:
http://www.elecraft.com/Apps/new_fil_docs/filter_apps.htm
Then, go back and tweak FL1 or the bF1txxx settings for the most natural
sounding TX audio. Wayne and I have found that the optimum TX BFO setting
is often 50-200Hz different than the best sounding RX BFO settings.
Monitoring the K2's SSB TX signal on another rig is the best way to
determine this. I use headphones on the other rig to prevent audio
feedback, and then compare how my voice sounds on the headphones to how I
really sound in person. Exposing one ear by removing that side of the
headphones, and cupping a hand between the mouth and exposed ear helps
you compare the real and transmitted audio - just as you have seen some
singers (on TV or film) do in the recording studio. The BFO settings in
CAL FIL can then be best determined for your particular voice and mic
characteristics. A tinny or bassy sounding mic can also be improved with
a little effort and time spent in CAL FIL.
For example:
In LSB, moving the BFO *lower* in freq. (further from the center of the
IF passband) will enhance the treble or higher voice characeristics.
Moving the BFO *higher* in freq. (closer to the center of the IF
passband) will make the audio sound more bassy.
In USB, do just the opposite to the BFO freq. for the same effect.
Always use a lower band (such as 80m or 40m) when doing this, to avoid
the confusing reversal of BFO settings that occurs on bands from 15m to
10m.
The point here is, that although the KSB2 SSB filter may be a little on
the narrow side, some attention to how well the CAL FIL BFO settings are
done can optimize the way the rig sounds in both SSB RX and TX.
Note that the FL1 or bF1txxx settings are always used for transmitting,
regardless of which filter FL2-FL4 is selected. This allows you to have
custom BFO settings for RX and TX. This is why we recommend you set
FL2=OP1 in CAL FIL, and then set this filter up for the most pleasing SSB
RX audio and use it for all normal SSB operations. The BFO setting for
FL1 that have been customized for the best sounding SSB TX audio, will be
automatically selected when you transmit.
One advantage of a narrow SSB filter is that more power is concentrated
into a smaller bandwidth TX signal, maximizing the punch of the QRP power
level.
For the best sounding RX SSB audio, you should also perform the 2nd FIL
mod that allows the LSB/USB and CW settings of L34 to be optimized.
See: http://www.elecraft.com/Apps/new_fil_docs/k2_2nd_xfil_ssb_mod.pdf
This mod takes four commonly available parts and about 15 minutes to do.
It will likely be phased into the next K2 revision. This mod affects ONLY
the SSB RX audio, and has no direct affect on the SSB TX audio.
Gary Surrency AB7MY
For Elecraft Technical Support, please use: [email protected]
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